bit_reverse_cplx.c

同样是浮点型的fft算法一样为vc开发的

/*
 *	DATE:05/30/2006
 *
 *	AUTHOR:CHEN PENG
 *
 *	VERSION:ORIGINAL 05/30/2006
 *			MODIFIED 06/20/2006
 */
 
/******************************************************************************\
*	FUNCTION:	void bit_reverse_cplx(int x[], int num)
*
*	AGRUMENTS:	x[num]	Input and output sequences. Size num complex
*						elements
*				
*				num		Number of complex elements in vector x. Must be
*						power of 2
*				
*	DESCRIPTION:	This routine is used to compute the bit-reverse or
*					bit-normal order corresponding to input vector x, 
*					with size num. Each complex value is with interleaved 
*					16-bit real and imaginary parts.
*
*	REQUIREMENTS:	1. 4 <= num <= 65536( num a power of 2)
*					2. x data is stored in the order real[0],image[0],real[1],...
*					3. x is aligned on a 4*num byte boundary 
*					4. The code is LITTLE ENDIAN
*
\******************************************************************************/

void bit_reverse_cplx(int x[], int num){
	int iBefore, iBehind, tempData, temph, templ, temp, i;
	int hBitRef, lBitRef, hBit, lBit;
	char hPos, lPos, bitMov;
	short nBits;
	nBits = 0;
	i = num;
	/* acquire bit numbers occupied by the size of x */
	while(i > 1){
		i >>= 1;
		nBits++;
	}
	hBitRef = 0x00000001 << (--nBits);
	lBitRef = 0x00000001;
	/*
	 *for each index, search for its corresponding bit-reversed index, then
	 *switch the indexed datas.
	 */
	for( iBefore = 1; iBefore < num; iBefore++ ){
		hPos = nBits;
		lPos = 0;
		hBit = hBitRef;
		lBit = lBitRef;
		bitMov = nBits;
		temp = 0;
		/* bit-reverse */
		while( hPos > lPos ){
			temph = iBefore & hBit;
			templ = iBefore & lBit;
			temph >>= bitMov;
			templ <<= bitMov;
			temp += temph + templ;
			hPos--;
			lPos++;
			bitMov -= 2;
			hBit >>= 1;
			lBit <<= 1;
		}
		if( hPos == lPos ){
			temph = iBefore & hBit;
			temp += temph;
		}
		/* data exchange */
		iBehind = temp;  
		if( iBehind < iBefore )
			continue;
		tempData = x[iBefore];
		x[iBefore] = x[iBehind];
		x[iBehind] = tempData;
	}
	return;	
}